Comprehend
Res Ipsa Loquitur
Because technically, it is plural.
What Jay said earlier is illuninating:
That is, as in Genesis 1:1
IN THE beginning God (plural) created (singular verb referring to a techically plural subject) the heaven and the earth.
In many languages, the singluar verb can refer to plural subjects and vice versa. There are many examples in Hebrew (I believe mostly for emphasis) and Greek (due to fluidity), but ifall the adjectives and verbs in reference to Elohim are in the singular (as Jay says, and I'm sure he's right) it must be on purpose.
I do think that the OP addresses the evolution of the term...
EDIT: I forgot also to note that many technically plural nouns may actually be conceptualized as singular - like "seas" may be just one "sea," but it's plural. There are many examples of this in Hebrew if I remember correctly...
Well, now I am interested... is there a major disagreement between different groups?
Do most Christians believe it is plural or singular?